1. Field of the Invention
This invention generally relates to systems and methods for directionally drilling a borehole. Certain embodiments relate to a system for directionally drilling a borehole that includes a continuously variable transmission that is configured to control relative rotation of one or more components of a biasing subsystem during drilling of the borehole.
2. Description of the Related Art
The following descriptions and examples are not admitted to be prior art by virtue of their inclusion within this section.
As downhole tools for oilfield applications become more complex, the control systems for controlling these tools have also increased in complexity. Many downhole tools attempt to control relative rotation through various means including electric, mechanical and hydraulic means. Examples for controlling relative rotation in a borehole also include measurement techniques that are performed during drilling such as mud-pulse telemetry, rotary steerable drilling systems, orientation of devices on coiled tubing, control of systems during casing while drilling, and in well completions. The systems themselves using direct or indirect control methods often form complicated clutching or servo-systems.
There are numerous issued U.S. Patents related to rotary steerable systems. One example of a rotary steerable system is the point-the-bit rotary steerable system. Several methods have been utilized to orient the axis of the bit in point-the-bit systems. Two common methods include deflecting a pipe and using universal joints.
One example of a point-the-bit rotary steerable system that includes universal joints is illustrated in U.S. Pat. No. RE29,526 to Jeter, which is incorporated by reference as if fully set forth herein. Jeter describes deviating the axis of a bit with relation to the drillstring. The offset is controlled allowing it to be reasonably stationary (non-rotating) within the earth's reference frame. Jeter also describes utilizing a universal joint that allows the bit sub, which connects the drill bit to the drillstring, to pivot a limited amount in any direction relative to the drill pipe. In particular, Jeter describes a universal connection for urging the bit sub to pivot in one direction thereby moving the axis of rotation of the bit out of alignment with the axis of rotation of the drill pipe to urge the bit to drill in a direction that will return the drillstring to the desired azimuthal direction and inclination. Jeter also describes allowing the axis of the lower member containing a bit to be offset with respect to the axis of the upper member and controlling the offset of the axis using fluid motors or cams.
Another example of a point-the-bit rotary steerable system that includes universal joints is illustrated in U.S. Pat. No. 5,113,953 to Noble, which is incorporated by reference as if fully set forth herein. Noble describes offsetting the axis of a bit-shaft with a universal joint and controlling the universal joint in relation to an earth reference frame to directionally drill. In addition, Noble describes utilizing an electric motor to provide control means.
An additional example of a point-the-bit rotary steerable system that includes universal joints is illustrated in U.S. Pat. No. 6,092,610 to Kosmala et al., which is incorporated by reference as if fully set forth herein. Kosmala et al. describe a universal joint system that is used to omni-directionally pivotally support a bit-shaft intermediate its upper and lower ends. In addition, the system described by Kosmala et al. includes a breaking device to provide controllability of the system. Kosmala et al. further describe the use of an electric motor coupled to a breaking mechanism to provide rotational control. A breaking mechanism is necessary when utilizing an electrical motor.
FIG. 1 provides an overview of an actively controlled rotary steerable system utilizing an electric motor described by Kosmala et al. System 26 includes tubular collar 32 coupled to threaded section 34, which allows connection to the drillstring. Sensor support section 40 is disposed within the tubular collar. Potential electronics system 41 such as a resistivity measurement system may be included within the sensor support section. In addition, sensor support section 40 may include receptacle 42 for housing magnetometers, accelerometers, and other electronics. The system may also include fluid energized turbine 48, which includes turbine stator 50. Turbine rotor 52 is coupled by turbine rotor output shaft 54 to the rotor of alternator 56. As further shown in FIG. 1, the system also includes transmission 58, electric motor 60, gearbox or transmission 61 that is driven by the motor, offsetting mandrel 62, rotary drive head 64 that contains eccentrically located positioning receptacle 66, which receives driven end 68 of bit shaft 70, and pivoting universal joint 72. As the turbine rotates, the alternator converts the rotary energy into electrical power utilized in electric motor 60. The electric motor provides a servo-control system for ensuring control of the offset created by universal joint 72 located between the tubular collar and the bit shaft.
It is noted that in the system described by Kosmala et al. the turbine rotor rotation rate is not controlled by the rotary steerable system, but is determined by fluid flow in the drilling system. This uncontrolled rotation is utilized to create power to rotate the electric motor. The motor's rotation is controlled through the use of a servo-control system.
Another example of a steerable drilling tool and system is illustrated in U.S. Pat. No. 5,617,926 to Eddison et al., which is incorporated by reference as if fully set forth herein. A conceptual drawing of the system is shown in FIG. 2. The system described by Eddison et al. includes universal joint 74 that is similar to the universal joint described by Jeter. The universal joint described by Eddison et al. is coupled with internal eccentric mass 76, j-slot orientation control mechanism 78, and offset mandrel 80. Additional description of the system shown in FIG. 2 can be found in U.S. Pat. No. 5,617,926 to Eddison et al.
Major limitations with this design exist in the implementation of the control mechanism and the application of the torque supplied by the eccentric weight. The eccentric weight provides it maximum torque when its center of gravity is at 90 degrees to the gravity vector when projected onto the radial axis in the tools reference frame. When the system is operating within maximum torque requirements, the system orientation vector for the drive shaft can only be controlled within a given quadrant. The orientation itself is a function of the resultant forces on the bit-shaft and is not controllable. Therefore, the control mechanism provides only limited control of the bit shaft orientation. The system becomes unstable when the torque required to orient the bit shaft is greater than that which can be supplied by the eccentric weight. These problems can be resolved with the implementation of the novel orientation mechanism described herein.
An alternative to the point-the-bit rotary steerable system has been introduced into the drilling market, which includes pointing the bit through the deflection of a shaft. Control of the shaft deflection is accomplished by various means. U.K. Patent Application No. GB 2 177 738 by Douglas, et al. provides an overview of how the concept of shaft deflection may be used in rotary steerable systems.
One example of such a system is illustrated in FIG. 3. As shown in FIG. 3, the drilling system includes drill collar 82 within borehole 84 being drilled, two spaced stabilizers 86 and 88, and control stabilizer 90. Control stabilizer 90 does not rotate with the collar and includes an activation mechanism for applying a controlled lateral force or displacement on the drill collar. The force causes bending in the collar and angular deflection 92 at bit 94. In other words, control stabilizer 90 applies to drill collar 82 a controlled lateral force or displacement (indicated by arrow 96) in order to deflect the latter between spaced supports 98 constituted by stabilizers 86 and 88. FIG. 3 illustrates the undeflected drill collar at 100 and the deflected drill collar at 102, the change in drilling direction being indicated by angle 92. Selective control of the activation mechanism force and direction relative to an earth's reference allows the system to provide steering control during the well drilling process.
Various control assemblies for shaft deflection have been designed to bend or deflect the drilling shaft laterally or radially within the housing. Several mechanisms for activation of the described directional biasing mechanism are described in U.K. Patent Application No. GB 2 177 738 by Douglas, et al. and U.S. Pat. No. 5,875,859 to Ikeda et al. and U.S. Pat. No. 6,244,361 to Comeau et al., which are incorporated by reference as if fully set forth herein.
The control mechanism described by Douglas et al. includes multiple actuators coupled to a non-rotating control stabilizer. As depicted in FIG. 4, an actuator assembly includes four individual actuators 104. These individual actuators 104 lie within annular space 106 between actuator casing 108 and actuator bridge member 110, and each actuator is disposed at equal intervals around the periphery. Individual actuators 104 create a force between casing 108 and actuator bridge member 110. The actuator bridge member resolves the relative rotation issues between the actuators and the shaft to be deflected. Douglas et al. envisioned the individual actuators to be flexible hydraulic tubes, which would be independently controlled to produce a specific output vector (magnitude and direction) at the shaft endpoint.
Ikeda et al. and Comeau et al. describe shaft deflection assemblies that include eccentric rings. Ikeda et al. and Comeau et al. both utilize shaft deflection to implement point-the-bit systems. The systems of Ikeda et al. and Comeau et al. differ from one another in the aspect of the drilling shaft assembly. While Comeau et al. utilizes a deflected shaft, the system proposed by Ikeda et al. contains a universal joint at the point of greatest stress in the shaft. This allows the system to bend without cyclically fatiguing the shaft. These differences are visible in FIGS. 5 and 6, which are taken from the patents issued to Ikeda et al. and Comeau et al, respectively. FIG. 5 illustrates the deflection and control mechanism described by Ikeda et al. FIG. 6 illustrates the deflection and control mechanism described by Comeau et al.
As shown in FIG. 5, the mechanism described by Ikeda et al. includes upper rotating shaft 112 for rotary drilling equipment and lower rotating shaft 114, which is connected to the upper rotating shaft and flexible joint 116. The mechanism also includes drill collar 118, which is co-axially connected to the distal end portion of lower rotating shaft 114 and drill bit 120, which is secured at the distal end of drill collar 118. Furthermore, upper rotating shaft 112 is connected to a rotating driving mechanism (not shown).
In addition, the mechanism includes cylinder-type housing 122, which encloses an outer peripheral surface of upper and lower rotating shafts 112 and 114 above drill collar 118 and lower sealing equipment 124, which is provided between the distal end portion of cylinder-type housing 122 and lower rotating shaft 114. The system shown in FIG. 5 also includes fulcrum bearing 126, which is located between cylinder-type housing 122 of lower sealing equipment 124 and lower rotating shaft 114 and receives the load from drill bit 120, double eccentric mechanism 128, which is mounted between cylinder type housing 122 above fulcrum bearing 126 and lower rotating shaft 114, cylinder-type component 130, which is fixed on an inner peripheral surface of cylinder type housing 122, first rotatable ring-formed component 132, which is located inside cylinder type component 130 and second ring-formed component 134, which is rotatably deposited inside the first ring-formed component.
The system shown in FIG. 5 further includes first harmonized reduction gear 136 which rotates first ring-formed component 132 located right above double eccentric mechanism 128, second harmonized reduction gear 138, which rotates second ring-formed component 134 being provided right below double eccentric mechanism 128, bearing 140 which supports the lower portion of upper rotating shaft 112, and upper seal 142 which is provided between the upper portion of cylinder type housing 122 and upper rotating shaft 112. The mechanism shown in FIG. 5 may be further configured as described in U.S. Pat. No. 5,875,859 to Ikeda et al.
As shown in FIG. 6, the mechanism of Comeau et al. includes drilling direction control device 144, which permits directional control over drilling bit 146 connected within the device during rotary drilling operations by controlling the orientation of the drilling bit. Drilling direction control device 144 includes rotatable drilling shaft 148, which is connectable or attachable to rotary drilling string 150 during the drilling operation. Housing 152 rotatably supports a length of drilling shaft 148 for rotation therein upon rotation of the attached drilling string 150. Device 144 also includes at least one distal radial bearing 154 and at least one proximal radial bearing 156. Each of the radial bearings 154 and 156 is contained within housing 152 for rotatably supporting the drilling shaft 148 radially at the location of that particular radial bearing. Distal radial bearing 154 preferably includes fulcrum bearing 158.
Preferably, device 144 further includes near bit stabilizer 160, which in the preferred embodiment is located adjacent to the distal end of housing 152 and coincides with the distal radial bearing location. Furthermore, device 144 includes drilling shaft deflection assembly 162, which may be located axially at any location or position between the distal end and the proximal end of the housing. Deflection assembly 162 is provided for bending drilling shaft 148 between the distal radial bearing location and the proximal radial bearing location. The device also includes at least distal thrust bearing 164 and at least one proximal thrust bearing 166. Each of the thrust bearings is contained within housing 152 for rotatably supporting drilling shaft 148 axially at the location of that particular thrust bearing. As a result of the thrust bearings, most of the weight on the drilling bit may be transferred into and through housing 152 as compared to through the drilling shaft of the device.
Device 144 also includes anti-rotation device 168 associated with housing 152 for restraining rotation of housing 152 within the wellbore upon rotary drilling. Preferably, the device further includes a distal seal or sealing assembly 170 and a proximal seal or sealing assembly 172. Distal seal 170 is radially positioned and provides a rotary seal between housing 152 and drilling shaft 148 at, adjacent or in proximity to the distal end of housing 152. Proximal seal 172 is radially positioned and provides a rotary seal between housing 152 and drilling shaft 148 at, adjacent or in proximity to the proximal end of housing 152. Additional details of the mechanism shown in FIG. 6 can be found in U.S. Pat. No. 6,244,361 to Comeau et al.
The control mechanisms described by Ikeda et al. and Comeau et al. include shaft deflection assemblies that include eccentric rings, as shown in FIGS. 7a and 7b. This type of assembly is known in the art. The assembly includes two eccentric rings, inner ring 174 and outer ring 176, which are capable of relative rotation. Relative rotation between the two eccentric rings results in a relative displacement between the center of the outer ring and the center of the inner ring. The system can be designed such that at 0 degrees of rotation, the centers of the two eccentric rings coincide, as shown in FIG. 7a. The rings have a maximum displacement between their centers at 180 degrees of relative rotation, as shown in FIG. 7b. Such a system provides the ability to impart a controlled deflection on the drilling shaft at the location of the assembly.
Both systems utilize harmonic drives to control the orientation of the eccentric ring systems. A harmonic drive is required for each ring. The drive system takes power from the relative rotation between the non-rotating sleeve and the drive shaft.
Push-the-bit rotary steerable systems utilize side force on near-bit assemblies to provide a deviation mechanism. Variations on the concept fall into two categories: synchronous systems and non-rotating systems.
Synchronous rotary drilling systems are illustrated in U.S. Pat. No. 5,265,682 to Russell et al., which is incorporated by reference as if fully set forth herein. One system described by Russell et al. includes a modulated bias unit, which is used to control the direction of the drilling assembly, and a control unit for modulating such bias unit. FIG. 8 provides a conceptual overview of the synchronous push-the-bit system. The bias unit includes hydraulic actuators 178 spaced apart around the periphery of the unit proximate bit connector 180 and a selector control valve (not shown). The selector control valve is coupled to hydraulic actuators 178 by hydraulic ports 182. Each actuator is capable of providing a force and outward displacement against the formation. The selector control valve modulates the fluid pressure supplied to each actuator in synchronism with rotation of the drill bit so that, as the drill bit rotates, each movable thrust member is displaced at the same selected rotational position. This displacement of the movable thrust members causes a constant relative thrust at a radial point in the borehole. The control valve includes two disks. One disk contains a port for each of the actuators. The second disk is rotationally controlled by the control sub to selectively activate each actuator at the prescribed position.
The control system for the synchronous system utilizes a downhole instrumentation package, which is roll stabilized with respect to the drillstring. Mounted impellers 184 rotate relative to the drill collar as a result of fluid flow. The impellers are mounted such that their relative rotation is in opposite directions. Control sub 186 is also mounted to the housing through bearings allowing for relative rotation. The impellers impart a controlled torque against the control sub housing through a clutching mechanism such as an electromagnetic clutch. Controlling the torque imparted by each impeller allows for the control sub to be rotationally controlled and non-rotating with respect to an earth reference frame.
A second group of push-the-bit systems exist that include non-rotating stabilizers. A side force is applied to the formation through a non-rotating assembly. Examples of such systems are illustrated in U.S. Pat. No. 5,979,570 to McLoughlin et al. and European Patent Application No. 0 744 526 A1 by Oppelt et al., which are incorporated by reference as if fully set forth herein. FIGS. 9a and 9b are schematic diagrams illustrating a push-the-bit system utilizing a non-rotating sleeve and eccentric rings. FIGS. 10a and 10b are schematic diagrams illustrating a push-the-bit system utilizing a non-rotating sleeve and hydraulic action.
As shown in FIG. 9a, this push-the-bit system is attached to adapter sub 188, which would in turn be attached to the drill string (not shown). The adapter sub is attached to inner rotatable mandrel 190 and may not be necessary if the drill string pipe threads match the device threads. This mandrel is free to rotate within inner eccentric sleeve 192. Inner eccentric sleeve 192 may be turned freely within an arc by a drive means (not shown) inside the outer eccentric housing or mandrel 194, as shown in FIGS. 9a and 9b. 
As further shown in FIG. 9a, inner rotating mandrel 190 is shown as being attached directly to drill bit 196. Outer housing 194 consists of a bore passing longitudinally through the outer sleeve which accepts the inner sleeve. The outer housing is eccentric on its outside clearly shown as “pregnant” portion 198. The pregnant portion or weighted side 198 of the outer housing forms the heavy side of the outer housing and is manufactured as a part of the outer sleeve. The pregnant housing contains the drive means for controllably turning the inner eccentric sleeve within the outer housing. Additionally, the pregnant housing may contain logic circuits, power supplies, hydraulic devices, and the like which are (or may be) associated with the “on demand” turning of the inner sleeve. Additional details of the system shown in FIGS. 9a and 9b can be found in U.S. Pat. No. 5,979,570.
As shown in FIGS. 10a and 10b, this push-the-bit system includes bit 198 coupled to hydraulic actuator assembly 200. The hydraulic actuator assembly is coupled to non-rotating sleeve assembly 202. The hydraulic actuator assembly may be configured such that a side force can be selectively applied to a formation (not shown) through non-rotating sleeve assembly 202. The amount and direction of the side force will vary depending on the direction in which drilling is desired. The amount and direction of the side force that is applied to the formation may be controlled by hydraulic control assembly 204, which is coupled to hydraulic actuator assembly 200. Additional details of the system shown in FIGS. 10a and 10b can be found in European Patent Application No. 0744526.
Rotary steerable systems all attempt to control the rotation of specific system components relative to an earth reference frame (gravity, magnetic vector, etc.). This attempt to control relative rotation is analogous to the control sought in other systems with specific types of transmission known as continuously variable transmissions (CVTs).
Continuously variable transmissions (CVTs) have existed for over 100 years. However, they are only today beginning to see widespread use as a fuel-saving technology in the automotive industry. For example, the technology was first introduced in 1886, but its practical automotive merits were not fully realized until Honda installed a CVT in its 1996 Civic HX.
Some light-weight automobiles are already using CVTs in which power is transferred by a belt in contact with one or more pulleys. However, CVTs that use belts (or sometimes chains) are limited to fairly light vehicles, usually those weighing under about 2,000 pounds. For example, the Ford Festiva and the Subaru Justy use a CVT. In the light passenger vehicles they are now being used in, CVTs provide high efficiency and thus boost fuel mileage while reducing emissions.